Bluetooth: Return RFCOMM session ptrs to avoid freed session

Unfortunately, the design retains local copies of the s RFCOMM
session pointer in various code blocks and this invites the erroneous
access to a freed RFCOMM session structure.

Therefore, return the RFCOMM session pointer back up the call stack
to avoid accessing a freed RFCOMM session structure. When the RFCOMM
session is deleted, NULL is passed up the call stack.

If active DLCs exist when the rfcomm session is terminating,
avoid a memory leak of rfcomm_dlc structures by ensuring that
rfcomm_session_close() is used instead of rfcomm_session_del().

Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

1 files changed, 56 insertions, 50 deletions

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index d9e97cf1792b..2b5c543638ba 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -69,7 +69,7 @@ static struct rfcomm_session *rfcomm_session_create(bdaddr_t *src,
                                                         u8 sec_level,
                                                         int *err);
 static struct rfcomm_session *rfcomm_session_get(bdaddr_t *src, bdaddr_t *dst);
-static void rfcomm_session_del(struct rfcomm_session *s);
+static struct rfcomm_session *rfcomm_session_del(struct rfcomm_session *s);
 
 /* ---- RFCOMM frame parsing macros ---- */
 #define __get_dlci(b)     ((b & 0xfc) >> 2)
@@ -108,10 +108,12 @@ static void rfcomm_schedule(void)
         wake_up_process(rfcomm_thread);
 }
 
-static void rfcomm_session_put(struct rfcomm_session *s)
+static struct rfcomm_session *rfcomm_session_put(struct rfcomm_session *s)
 {
-        if (atomic_dec_and_test(&s->refcnt))
-                rfcomm_session_del(s);
+        if (s && atomic_dec_and_test(&s->refcnt))
+                s = rfcomm_session_del(s);
+
+        return s;
 }
 
 /* ---- RFCOMM FCS computation ---- */
@@ -631,7 +633,7 @@ static struct rfcomm_session *rfcomm_session_add(struct socket *sock, int state)
         return s;
 }
 
-static void rfcomm_session_del(struct rfcomm_session *s)
+static struct rfcomm_session *rfcomm_session_del(struct rfcomm_session *s)
 {
         int state = s->state;
 
@@ -648,6 +650,8 @@ static void rfcomm_session_del(struct rfcomm_session *s)
 
         if (state != BT_LISTEN)
                 module_put(THIS_MODULE);
+
+        return NULL;
 }
 
 static struct rfcomm_session *rfcomm_session_get(bdaddr_t *src, bdaddr_t *dst)
@@ -666,7 +670,8 @@ static struct rfcomm_session *rfcomm_session_get(bdaddr_t *src, bdaddr_t *dst)
         return NULL;
 }
 
-static void rfcomm_session_close(struct rfcomm_session *s, int err)
+static struct rfcomm_session *rfcomm_session_close(struct rfcomm_session *s,
+                                                   int err)
 {
         struct rfcomm_dlc *d;
         struct list_head *p, *n;
@@ -685,7 +690,7 @@ static void rfcomm_session_close(struct rfcomm_session *s, int err)
         }
 
         rfcomm_session_clear_timer(s);
-        rfcomm_session_put(s);
+        return rfcomm_session_put(s);
 }
 
 static struct rfcomm_session *rfcomm_session_create(bdaddr_t *src,
@@ -737,8 +742,7 @@ static struct rfcomm_session *rfcomm_session_create(bdaddr_t *src,
         if (*err == 0 || *err == -EINPROGRESS)
                 return s;
 
-        rfcomm_session_del(s);
-        return NULL;
+        return rfcomm_session_del(s);
 
 failed:
         sock_release(sock);
@@ -1127,7 +1131,7 @@ static void rfcomm_make_uih(struct sk_buff *skb, u8 addr)
 }
 
 /* ---- RFCOMM frame reception ---- */
-static int rfcomm_recv_ua(struct rfcomm_session *s, u8 dlci)
+static struct rfcomm_session *rfcomm_recv_ua(struct rfcomm_session *s, u8 dlci)
 {
         BT_DBG("session %p state %ld dlci %d", s, s->state, dlci);
 
@@ -1136,7 +1140,7 @@ static int rfcomm_recv_ua(struct rfcomm_session *s, u8 dlci)
                 struct rfcomm_dlc *d = rfcomm_dlc_get(s, dlci);
                 if (!d) {
                         rfcomm_send_dm(s, dlci);
-                        return 0;
+                        return s;
                 }
 
                 switch (d->state) {
@@ -1172,25 +1176,14 @@ static int rfcomm_recv_ua(struct rfcomm_session *s, u8 dlci)
                         break;
 
                 case BT_DISCONN:
-                        /* rfcomm_session_put is called later so don't do
-                         * anything here otherwise we will mess up the session
-                         * reference counter:
-                         *
-                         * (a) when we are the initiator dlc_unlink will drive
-                         * the reference counter to 0 (there is no initial put
-                         * after session_add)
-                         *
-                         * (b) when we are not the initiator rfcomm_rx_process
-                         * will explicitly call put to balance the initial hold
-                         * done after session add.
-                         */
+                        s = rfcomm_session_close(s, ECONNRESET);
                         break;
                 }
         }
-        return 0;
+        return s;
 }
 
-static int rfcomm_recv_dm(struct rfcomm_session *s, u8 dlci)
+static struct rfcomm_session *rfcomm_recv_dm(struct rfcomm_session *s, u8 dlci)
 {
         int err = 0;
 
@@ -1215,12 +1208,13 @@ static int rfcomm_recv_dm(struct rfcomm_session *s, u8 dlci)
                         err = ECONNRESET;
 
                 s->state = BT_CLOSED;
-                rfcomm_session_close(s, err);
+                s = rfcomm_session_close(s, err);
         }
-        return 0;
+        return s;
 }
 
-static int rfcomm_recv_disc(struct rfcomm_session *s, u8 dlci)
+static struct rfcomm_session *rfcomm_recv_disc(struct rfcomm_session *s,
+                                               u8 dlci)
 {
         int err = 0;
 
@@ -1250,10 +1244,9 @@ static int rfcomm_recv_disc(struct rfcomm_session *s, u8 dlci)
                         err = ECONNRESET;
 
                 s->state = BT_CLOSED;
-                rfcomm_session_close(s, err);
+                s = rfcomm_session_close(s, err);
         }
-
-        return 0;
+        return s;
 }
 
 void rfcomm_dlc_accept(struct rfcomm_dlc *d)
@@ -1674,11 +1667,18 @@ drop:
         return 0;
 }
 
-static int rfcomm_recv_frame(struct rfcomm_session *s, struct sk_buff *skb)
+static struct rfcomm_session *rfcomm_recv_frame(struct rfcomm_session *s,
+                                                struct sk_buff *skb)
 {
         struct rfcomm_hdr *hdr = (void *) skb->data;
         u8 type, dlci, fcs;
 
+        if (!s) {
+                /* no session, so free socket data */
+                kfree_skb(skb);
+                return s;
+        }
+
         dlci = __get_dlci(hdr->addr);
         type = __get_type(hdr->ctrl);
 
@@ -1689,7 +1689,7 @@ static int rfcomm_recv_frame(struct rfcomm_session *s, struct sk_buff *skb)
         if (__check_fcs(skb->data, type, fcs)) {
                 BT_ERR("bad checksum in packet");
                 kfree_skb(skb);
-                return -EILSEQ;
+                return s;
         }
 
         if (__test_ea(hdr->len))
@@ -1705,22 +1705,23 @@ static int rfcomm_recv_frame(struct rfcomm_session *s, struct sk_buff *skb)
 
         case RFCOMM_DISC:
                 if (__test_pf(hdr->ctrl))
-                        rfcomm_recv_disc(s, dlci);
+                        s = rfcomm_recv_disc(s, dlci);
                 break;
 
         case RFCOMM_UA:
                 if (__test_pf(hdr->ctrl))
-                        rfcomm_recv_ua(s, dlci);
+                        s = rfcomm_recv_ua(s, dlci);
                 break;
 
         case RFCOMM_DM:
-                rfcomm_recv_dm(s, dlci);
+                s = rfcomm_recv_dm(s, dlci);
                 break;
 
         case RFCOMM_UIH:
-                if (dlci)
-                        return rfcomm_recv_data(s, dlci, __test_pf(hdr->ctrl), skb);
-
+                if (dlci) {
+                        rfcomm_recv_data(s, dlci, __test_pf(hdr->ctrl), skb);
+                        return s;
+                }
                 rfcomm_recv_mcc(s, skb);
                 break;
 
@@ -1729,7 +1730,7 @@ static int rfcomm_recv_frame(struct rfcomm_session *s, struct sk_buff *skb)
                 break;
         }
         kfree_skb(skb);
-        return 0;
+        return s;
 }
 
 /* ---- Connection and data processing ---- */
@@ -1866,7 +1867,7 @@ static void rfcomm_process_dlcs(struct rfcomm_session *s)
         }
 }
 
-static void rfcomm_process_rx(struct rfcomm_session *s)
+static struct rfcomm_session *rfcomm_process_rx(struct rfcomm_session *s)
 {
         struct socket *sock = s->sock;
         struct sock *sk = sock->sk;
@@ -1878,17 +1879,20 @@ static void rfcomm_process_rx(struct rfcomm_session *s)
         while ((skb = skb_dequeue(&sk->sk_receive_queue))) {
                 skb_orphan(skb);
                 if (!skb_linearize(skb))
-                        rfcomm_recv_frame(s, skb);
+                        s = rfcomm_recv_frame(s, skb);
                 else
                         kfree_skb(skb);
         }
 
-        if (sk->sk_state == BT_CLOSED) {
+        if (s && (sk->sk_state == BT_CLOSED)) {
                 if (!s->initiator)
-                        rfcomm_session_put(s);
+                        s = rfcomm_session_put(s);
 
-                rfcomm_session_close(s, sk->sk_err);
+                if (s)
+                        s = rfcomm_session_close(s, sk->sk_err);
         }
+
+        return s;
 }
 
 static void rfcomm_accept_connection(struct rfcomm_session *s)
@@ -1925,7 +1929,7 @@ static void rfcomm_accept_connection(struct rfcomm_session *s)
                 sock_release(nsock);
 }
 
-static void rfcomm_check_connection(struct rfcomm_session *s)
+static struct rfcomm_session *rfcomm_check_connection(struct rfcomm_session *s)
 {
         struct sock *sk = s->sock->sk;
 
@@ -1944,9 +1948,10 @@ static void rfcomm_check_connection(struct rfcomm_session *s)
 
         case BT_CLOSED:
                 s->state = BT_CLOSED;
-                rfcomm_session_close(s, sk->sk_err);
+                s = rfcomm_session_close(s, sk->sk_err);
                 break;
         }
+        return s;
 }
 
 static void rfcomm_process_sessions(void)
@@ -1975,15 +1980,16 @@ static void rfcomm_process_sessions(void)
 
                 switch (s->state) {
                 case BT_BOUND:
-                        rfcomm_check_connection(s);
+                        s = rfcomm_check_connection(s);
                         break;
 
                 default:
-                        rfcomm_process_rx(s);
+                        s = rfcomm_process_rx(s);
                         break;
                 }
 
-                rfcomm_process_dlcs(s);
+                if (s)
+                        rfcomm_process_dlcs(s);
 
                 rfcomm_session_put(s);
         }